1. Field of the Invention
This invention relates generally to cryogenic front-end receivers and, more particularly, to cryogenic front-end receivers of minimal size based on super-conducting elements, low thermal transmission interconnects, self-resonating filters and low dissipated power profile.
2. Description of the Related Art
Until the late 1980s, the phenomenon of superconductivity found very little practical application due to the need to operate at temperatures in the range of liquid helium. In the late 1980s ceramic metal oxide compounds containing rare earth elements began to radically alter this situation. Prominent examples of such materials include YBCO (yttrium-barium-copper oxides, see WO88/05029 and EP-A-0281753), TBCCO (thallium-barium-calcium-copper oxides, see U.S. Pat. No. 4,962,083) and TPSCCO (thallium-lead-strontium-calcium-copper oxides, see U.S. Pat. No. 5,017,554). All of the above publications are incorporated by reference for all purposes as if fully set forth herein.
These compounds, referred to as HTS (high temperature superconductor) materials, exhibit superconductive properties at temperatures sufficiently high enough to permit the use of liquid nitrogen as a coolant. Because liquid nitrogen at 77 K (196xc2x0 C./321xc2x0 F.) cools twenty times more effectively than liquid helium and is ten times less expensive, a wide variety of potential applications began to hold the promise of economic feasibility. For example, HTS materials have been used in applications ranging from diagnostic medical equipment to particle accelerators.
Currently one of the fastest growing applications for superconductivity lies in the area of electronics and associated microwave engineering, due to the astronomical growth in the telecommunications industry and the increased use of consumer electronics by the general population. In spite of the recent advances in superconductivity, however, size, cost and power requirements have limited the commercial use of this promising technology in all but high-end applications such as space instrumentation and military applications.
An essential component of many electronic devices, and particularly in the communications field, is the filter element. HTS filters have significant advantages in extremely low in-band insertion loss, high off-band rejection and steep skirts due to the extremely low radio frequency (RF) loss in the HTS materials.
However, the conventional transmission line HTS filters, having conventional HTS resonators (such as strip line resonators) as building blocks, require a large substrate area due to the area requirement that at least one dimension of the resonator be equal to approximately half a wavelength (i.e. xcex/2). See, for example, U.S. Pat. No. 5,616,538 (incorporated by reference for all purposes as if fully set forth herein). Thus, in conventional low frequency HTS filters having multiple poles and coupled with conventional semiconductor electronic components, such as gallium arsenide (GaAs) amplifiers, the cryogenic coolers required to cool the HTS materials to below their critical temperature (Tc) are relatively large and require heat lifts of at least 6 watts at 80 K at an ambient temperature of 20xc2x0 C.
FIG. 1 is a perspective view of such a conventional prior art cryogenic receiver. The overall integrated package consists of several distinct elements. The connectors 110 are used for bringing power and RF signals in and out of the cryoelectronic section, which consists of a dewar assembly 120 containing cryoelectronic components 130 such as RF filters and amplifiers. The dewar assembly 120 is the vacuum cavity necessary to reduce convective heat loading to the cryoelectronic components from molecules within the dewar assembly 120. A cryogenic source, in this case a cooler 140, provides the cooling for the cryoelectronic section. The enclosure 150 is an outer package containing the previously described elements as well as circuit boards 160 which provide control functions for the cooler and other error or failure detection and alarms, and a fan 170 for cooling the circuit boards 160.
The size of a conventional unit, as illustrated in FIG. 1, is typically on the order of at least about 15 inches widexc3x9720 inches longxc3x9710 inches deep (about 38.1xc3x9750.8xc3x9725.4 cm). The large size and weight of these conventional units stems predominately from the cooling required due to the physical size of the cryoelectronic section, the power required for the amplifiers, and additional convective heat flow from the RF transitions (normally coaxial cables with connectors), from ambient conditions into the dewar assembly 120. The physical size, weight and total operating power supplied to the unit is thus dominated by the cooler 140 and dewar assembly 120. For the conventional unit, the cooling lift required per channel is about 1 W when operated at 20xc2x0 C., thus the total operational power needed for the cooler 140 alone is  greater than 125 W.
Examples of conventional units are the Superfilter(trademark) Systems available from Superconductor Technologies Inc., Santa Barbara, Calif. (see www.suptech.com for more information), and the ClearSite(trademark) systems available from Conductus Inc., Sunnyvale, Calif. USA (see www.conductus.com for more information).
The large size and weight of these conventional units substantially limits the application of this technology. One such application is a tower top application in which a receiver front-end is mounted onto an antenna of a cellular or similar base station, such as those disclosed in U.S. Pat. No. 6,104,934 (incorporated by reference for all purposes as if fully set forth herein). The size and cooling requirements of the disclosed receiver are such that the cooling unit must be placed somewhere adjacent the antenna, and is not combinable with the electronics into an integrated unit.
For miniaturization purposes, the components comprising the greatest real estate needed are the cooler 140, cryoelectronic components 130 and dewar assembly 120.
One way to reduce the real estate requirements of a cryoelectronic front-end receiver is to employ lumped element architecture based on conventional HTS filters. These filters can be made to operate at frequencies below 5 GHz with a somewhat more compact physical size; however, filter performance of these conventional lumped element HTS filters is generally limited by intermodulation products and insertion loss.
The use of devices containing HTS filters presents other design problems. For example, the interconnects typically utilized to connect the cryogenic portion of the device (usually a dewar containing the HTS filter under vacuum) to other electronic components are long coaxial cables. These long cables, because of their length, exhibit low thermal transmission, which is highly desirable in a cryogenic system where keeping components cold is critical. However, these long cable lines also exhibit RF losses, thus contributing to degradation in RF performance (i.e. an increase in the signal-to-noise ratio). To compound problems even further, the long cables also require the dewar of the cryogenic portion of the device to be larger in volume, which requires a design capable of maintaining the vacuum necessary over the life of the unit, which is more difficult to achieve.
There has been a long felt need, as well as numerous attempts by persons of ordinary skill in the art, to reduce the size of filter elements constructed of HTS materials. U.S. Pat. No. 6,108,569, incorporated by reference herein for all purposes as if fully set forth, discloses the use of self-resonant spiral resonators to reduce the size of HTS material filters and concurrently solves cross-talk and connection problems. In spite of the great potential for miniaturization afforded by significant recent technological advances, the problems of vacuum degradation, high thermal transmission, and high dissipated power semiconductor devices, have resulted in less than optimum performance and yielded increased cooling costs.
Furthermore, conventional cryogenic front-end receivers require substantial time to manually tune the filters comprising a critical function of the unit. Since the resonating filters in a conventional filter construction do not each vary in a lock-stepped fashion, each pole of the filter must be individually tuned and the tuning of each pole affects every other pole in the filter array. The tuning process can typically take days to perform.
Moreover, conventional cryogenic front-end receivers also require the outgassing of molecules that adhere to the device walls during the manufacturing process. Typically, this problem is overcome by simply heating the device slowly over an extended period of time to outgas the gases, such as residual oxygen, nitrogen, carbon dioxide, argon, water vapor. The process normally takes days to complete, because the temperatures necessary to outgas the device walls in a short time period would damage the compressor motor comprising part of the cryogenic unit.
The prior art lacks a cryogenic front-end receiver of reduced size capable of being employed adjacent to or integrated with a receiver and/or transmitter.
The prior art also lacks a cryogenic front-end receiver with interconnections between the dewar and the cryogenic coolers exhibiting an extremely low thermal transmission to further thermally isolate the dewar.
The prior art additionally lacks a cryogenic front-end receiver having interconnections employing a thermal break material and a self-tuning reduced length for reducing RF losses and improving degradation in RF performance.
The prior art further lacks a cryogenic front-end receiver having reduced power consumption capabilities.
The prior art lacks a cryogenic front-end receiver employing reduced substrate size resonating filters made of HTS materials and resonating at frequencies below 5 GHz.
The prior art lacks a method for outgassing a vacuum dewar employing differential heating of the dewar assembly.
The prior art lacks a cryogenic front-end receiver capable of being tuned by varying the internal operating temperature of the front-end receiver.
The present invention has been made in view of the above circumstances and has as an aspect a cryogenic front-end receiver.
A further aspect of the present invention can be characterized as a cryogenic device, the device including a cryogenic electronic portion and a non-cryogenic electronic portion further including a thermal break section.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention can be characterized, according to one aspect, as a cryogenic front-end unit, the unit including a cryogenic electronic unit, wherein the cryogenic unit includes a input signal interface and output signal interface. A cryogenic cooler is in thermal communication with the cryogenic electronic unit. The cryogenic unit further includes an input signal interconnect that is connected to the input signal interface and an output signal interconnect that is connected to the output signal interface.
Another aspect of the present invention can be characterized as a cryogenic device including a cryogenic electronic portion, a non-cryogenic electronic portion and an interconnect connecting the cryogenic and non-cryogenic electronic portions, wherein the interconnect comprises a thermal break between cryogenic and non-cryogenic electronic portions.
A further aspect of the present invention can be characterized as a cryogenic device including a cryogenic electronic portion contained within a vacuum dewar assembly, the cryogenic electronic portion having an input end and an output end, and an ambient to cryogenic input connector having an ambient end passing through the vacuum dewar assembly to a cryogenic end connected to the input end of the cryogenic electronic portion. A cryogenic to ambient output connector with a cryogenic end connected to the output end of the cryogenic electronic portion, passes through the vacuum dewar assembly to an ambient end. A cryogenic source is connected to the vacuum dewar assembly so as to be in intimate contact with the cryogenic electronic portion, which has an input end and an output end. The cryogenic electronic portion includes at least one of a high temperature superconductor filter element and a cryogenic active semiconductor circuit (such as a low-noise amplifier). The input end of the cryogenic electronic portion is connected to the cryogenic end of the input connector and the output end of the cryogenic electronic portion is connected to the cryogenic end of the output connector. In the event that an active semiconductor circuit is used, that active semiconductor circuit should produce a total dissipated power into the cryogenic electronic portion of less than about 850 mW. The cryogenic device has a maximum cooler lift of less than about 3 W at 80 K at an ambient temperature of 20xc2x0 C.
Stated another way, this aspect of the present invention relates to a cryogenic device comprising:
(1) a cryogenic electronic portion contained within a vacuum dewar assembly, the cryogenic electronic portion having an input end and an output end;
(2) an ambient to cryogenic input connector having an ambient end passing through the vacuum dewar assembly to a cryogenic end connected to the input end of the cryogenic electronic portion,
(3) a cryogenic to ambient output connector having a cryogenic end connected to the output end of the cryogenic electronic portion, passing through the vacuum dewar assembly to an ambient end; and
(4) a cryogenic source connected to the vacuum dewar assembly so as to be in intimate contact with the cryogenic electronic portion, wherein:
(i) the cryogenic electronic portion comprises at least one of a high temperature superconductor filter element and a cryogenic active semiconductor circuit,
(ii) an active semiconductor circuit, if present, produces a total dissipated power into the cryogenic electronic portion of less than about 850 mW, and
(iii) the cryogenic device has a maximum cooler lift of less than about 3 W at 80 K at an ambient temperature of 20xc2x0 C.
Another aspect of the present invention can be characterized as a cryogenic receiver in which the cryogenic electronic portion of the above-mentioned cryogenic device comprises a high temperature superconductor filter element having an input end and an output end, and an active semiconductor circuit having an input end and an output end, wherein the input end of the active semiconductor circuit is connected to the cryogenic end of the input connector via the high temperature superconductor filter element. The input end of the filter element is connected to the cryogenic end of the input connector and the output end of the filter element is connected to the input end of the active semiconductor circuit.
Stated another way, this other aspect relates to a cryogenic receiver in which the cryogenic electronic portion of the above-mentioned cryogenic device comprises a high temperature superconductor filter element having an input end and an output end, and an active semiconductor circuit having an input end and an output end, wherein:
the input end of the active semiconductor circuit is connected to the cryogenic end of the input connector via the high temperature superconductor filter element;
the input end of the filter element is connected to the cryogenic end of the input connector; and
the output end of the filter element is connected to the input end of the active semiconductor circuit.
A still further aspect of the present invention can also be characterized as a cryogenic receiver including a cryogenic electronic portion contained within a vacuum dewar assembly, the cryogenic electronic portion having an input end and an output end. An ambient to cryogenic input connector having an ambient end passes through the vacuum dewar assembly to a cryogenic end connected to the input end of the cryogenic electronic portion, and a cryogenic to ambient output connector having a cryogenic end connected to the output end of the cryogenic electronic portion passes through the vacuum dewar assembly to an ambient end. The cryogenic receiver further comprises a cryogenic source connected to the vacuum dewar assembly so as to be in intimate contact with the cryogenic electronic portion. The cryogenic electronic portion additionally includes a high temperature superconductor filter element having an input end and an output end, and an active semiconductor circuit having an input end and an output end. The input end of the filter element is connected to the cryogenic end of the input connector and the output end of the filter element is connected to the input end of the active semiconductor circuit. The output end of the active semiconductor circuit is connected to the cryogenic end of the output connector and the active semiconductor circuit produces a total dissipated power into the cryogenic electronic portion of less than about 850 mW. The cryogenic receiver has a maximum cooler lift of less than about 3 W at 80 K at an ambient temperature of 20xc2x0 C.
Stated another way, this still further aspect of the present invention also relates to a cryogenic receiver comprising:
(1) a cryogenic electronic portion contained within a vacuum dewar assembly, the cryogenic electronic portion having an input end and an output end;
(2) an ambient to cryogenic input connector having an ambient end passing through the vacuum dewar assembly to a cryogenic end connected to the input end of the cryogenic electronic portion,
(3) a cryogenic to ambient output connector having a cryogenic end connected to the output end of the cryogenic electronic portion, passing through the vacuum dewar assembly to an ambient end; and
(4) a cryogenic source connected to the vacuum dewar assembly so as to be in intimate contact with the cryogenic electronic portion, wherein:
(i) the cryogenic electronic portion comprises:
(a) a high temperature superconductor filter element having an input end and an output end, and
(b) an active semiconductor circuit having an input end and an output end,
(ii) the input end of the filter element is connected to the cryogenic end of the input connector,
(iii) the output end of the filter element is connected to the input end of the active semiconductor circuit,
(iv) the output end of the active semiconductor circuit is connected to the cryogenic end of the output connector,
(v) the active semiconductor circuit produces a total dissipated power into the cryogenic electronic portion of less than about 850 mW, and
(vi) the cryogenic receiver has a maximum cooler lift of less than about 3 W at 80 K at an ambient temperature of 20xc2x0 C.
The reader should note that when one xe2x80x9ccomponentxe2x80x9d is connected to another xe2x80x9ccomponent,xe2x80x9d only a sequence is implied and, as such, other components may be connected in between. For example, input connector-filter element-active semiconductor-output connector is a sequence that can be interrupted by other components. It is generally accepted practice to keep the number of components in the vacuum dewar assembly to a minimum (e.g., to reduce cooling requirements), so it is desirable to have a direct connection from the input connector to the filter element, the filter element to the active semiconductor device, and the active semiconductor device to the output connector, as discussed in further detail below.
With the combination of the HTS filters (particularly those based on self-resonating spiral resonators), low dissipated power semiconductor devices (that operate effectively under the required cryogenic conditions) and the interconnects as mentioned above, much smaller cryogenic devices (such as low noise receivers) can be constructed and cooled by smaller cryogenic since these devices require cooler lifts of less than about 3 watts, more preferably less than about 2 watts, and still more preferably about 1 watt or less, to cool the cryoelectronic section to 80 K at an ambient temperature of 20xc2x0 C. In other words, the present invention provides miniature cryogenic devices delivering optimum performance at minimal size and cooling cost.
An additional benefit to the miniaturization enabled by the present invention is a significant reduction in the heat budget of the operating unit, which has a direct correlation to improved cryocooler efficiency, increased system operational life and reliability, and reduced energy consumption and operating costs.
The present invention also provides a method of tuning a cryogenic receiver comprising a high temperature superconducting filter element, said cryogenic receiver being programmed to operate at a specified operating frequency at a specified temperature, comprising the step of altering the specified operating temperature to induce a shift in the operating frequency of the cryogenic receiver.
This invention also provides a communications tower having an integrated antenna assembly located at the top of the tower, and a telecommunications network utilizing such a communications tower.
These and other features and advantages of the present invention will be more readily understood by those of ordinary skill in the art from the following detailed description. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. For example, it is to be appreciated that certain features of the invention which are, for clarity, described below in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination.